An oscillation gyro as one of quartz oscillators is used in a gyroscope of a movable body such as an aircraft or a vehicle, a navigation system of an automobile, a hand movement detection device of a video camera, or the like.
As this oscillation gyro, there is generally a tuning fork type quartz gyro with two or three tines (which will be appropriately abbreviated to as an oscillation gyro).
The tuning fork type quartz gyro with two tines is constituted of a first oscillating body having a driving piezoelectric element provided thereto and a second oscillating body having a detection piezoelectric element provided thereto, and the tuning fork type quartz gyro with three tines is constituted of first and second oscillating bodies each having a driving piezoelectric element provided thereto and a third oscillating body having a detection piezoelectric element provided thereto.
For example, the tuning fork type quartz gyro with two tines excites the oscillating body (a driving leg) having a driving electrode provided thereto to resonate the oscillating body (a detection leg) having a detection electrode provided thereto in the same direction as an exciting direction. When a quartz oscillator configured by accommodating this tuning fork type quartz oscillating piece with two-tines in a package rotates, the oscillating body having the detection electrode provided thereto oscillates in a direction perpendicular to the exciting direction by a Coriolis force received by rotation, and by detecting this oscillation by the detection electrode, an angular speed at which the quartz oscillator rotates can be detected.
Further, since the oscillation gyro integrates the angular speed to calculate a rotation angle, errors in the angular speed are accumulated, and this accumulated error becomes an error in angle. Therefore, in order to improve a measurement accuracy of the oscillation gyro, errors in the angular speed must be reduced.
As a first factor which produces an error in angular speed, there is a processing method of a quartz oscillating piece. In general, as to the quartz oscillating piece, a tabular quartz plate having a corrosion-proof membrane pattern formed thereon is wet-etched to manufacture an oscillating piece having a desired shape matching with the corrosion-proof membrane pattern, but the quartz has an etching anisotropy, processing cannot be performed to obtain a shape equal to the corrosion-proof membrane pattern at the time of wet etching, and an etching residue remains at a part of an etched end surface. In case of the fork quartz oscillator, since this etching residue remains on a side of the oscillating body matching with the exciting direction, the oscillating body is prevented from oscillating in the exciting direction. As a result, in a state where the quartz oscillator is not rotated, the oscillating body does not linearly oscillate in the exciting direction but oscillates in an elliptic trajectory pattern, and hence this oscillation component is detected as oscillation due to the Coriolis force in some cases.
Various technologies which oscillate the oscillating body in one direction have been developed with respect to the above-described factor.
For example, Patent Reference 1 discloses a technology of a characteristic adjustment method of an angular speed sensor which applies an alternating-current voltage to a driving electrode in a first oscillating body or a second oscillating body in a state where an angular speed is not given to the angular speed sensor as an oscillation gyro, and slides a tape in which a polishing agent is embedded on an edge line (a corner portion) in the first oscillating body or the second oscillating body in such a manner that an output signal from a detection electrode at this moment becomes substantially zero, thereby providing a ground portion.
When this technology is used, a ground portion having surface roughness of 2 μm or below can be provided on the edge line of the oscillating body, the balance of each oscillating body can be precisely redressed, and an output signal in a state where no angular speed is given can be approximated to substantially zero.
Moreover, as a second factor which causes an error in an angular speed, there is a change in temperature. Even if the balance of each oscillating body is precisely redressed at a predetermined temperature (which is generally an ordinary temperature) to oscillate each oscillating body in one direction without rotating a quartz oscillator, when a temperature varies, each oscillating body oscillates in an elliptic trajectory pattern, and this oscillation component is detected as oscillation due to a Coriolis force.
It is to be noted that characteristics that an output value varies in accordance with a change in temperature are called temperature drift characteristics, the second factor is the temperature drift characteristics attributed to a quartz oscillating piece, and the temperature drift characteristics must be stabilized. However, a mechanism of occurrence of the temperature drift characteristics has not been technically explained, and a technology of improving the temperature drift characteristics does not exist.
Patent Reference 1: Japanese Patent Application Laid-open No. 2002-243451